Loud-speaker



June 10, 1930. M. CJHOPKINS 6 LOUD SPEAKER Original Filed July 24. i925 2 Sheets-Sheet 1 {NVENTOR v r C Hop/(m ATTORNEY,

June 10,1930. M. c. HOPKINS 1,763,050

LOUD SPEAKER.

Original Filed-M1 124, 1926 2 sheets-sheep 2 WW M M w M j Patented June 10, 1930 UNITED STATES PATENT OFFICE MARCUS'C. HOPKINS, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO HOP- KINS CORPORATION, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF DELA- WARE LOUD-SPEAKER Application filed July 24, 1926, Serial Jim 124,867. Renewed March 22, 1930.

The present invention relates to loud speakers of the type disclosed in my copending application, Serial No. 77,033, filed December 22, 1925. The loud speaker disclosed in that application comprises a central relatively light and stiff diaphragm or tympanum, preferably conical in shape, and a surrounding external sound board or resonator having greater mass than that of the central diaphra m.

The connection between the central iaphragm and the external resonator or sound board is such tln. b the central diaphragm will resound to the relatively high frequencies and will efficiently reproduce the high tones or sounds, and the relatively low frequencies will be transmitted through said connection to the sound board so that it will respond to the relatively low frequencies and will efficiently reproduce them.

tion is to provide a loud speaker of the foregoing type having 'a sound board formed of cork.

I have found that two factors are of prima ry importance in the selection of a material suitable for use in a sound board of a loud speaker of this type. These factor are the weight of the material and its elasticity or r flexibility. While the wood sound board of my prior application Serial No. 77,033 is particularly suitable for use in loud speakers of the large sizes, it is not as satisfactory as cork in smaller sizes, where the diameter of the rim is 24 inches or less. In a copending application, Serial No. 87,491, I have disclosed and- 'claimed a loud speaker in which the sound board is formed of synthetic lumber. By synthetic lumber I mean relatively rigid 40 sheets or boards made. from fibers that have been separated, in part, at least, and re-assembled in a hetreogeneous arrangement in a new assembly. The rigidity of synthetic lumber may be regulated by varying the pressure applied in the press in re-assembling the fiber, but it is difficult to obtain a product satisfactory in other ways which will be as flexible as cork sheets.

I, therefore, consider cork the best substance available for the construction of the The principal object of the present inven-- rim of a loud speaker of small diameter, afnd a vibratory resonator or sound board 2 by means of a semi-flexible coupling,"shown in Fig.3. The conical diaphragm 1 is preferably made of cover paper, out and folded to shape and glued along a radial seam. Near the outer edge of the cone thus formed, the paper is creased and then folded up to form a forwardly flaring brim 3 (Fig. 3). This brim naturally assumes an angle to the plane of the base equal to the angle between the radial elements .of the cone and that base. The outer edge portion of the brim 3 is preferably glued to the inner circular edge of the resonator or sound board 2. For this purpose the inner circular edge of the sound board is tapered as shown at 4 and the outer edge portion of the brim 3 seats upon. and is glued to l the tapering surface thus formed. In glufing'o'r cementing the brim to the beveled edge 4 it is important that a part of the brim be leftfree to form a hinge on which the cone may float. Thus with a brim 4 wide the cementedportion may have a width of of an inch more or less and the remainder of the brim may be left free to swing.

The resonator or sound board 2 in accordance with this invention, is made of cork.

' The vibratory actuating force is applied to the apex of the conical diaphragm by means of a rod or wire-5 which is adapted to be maintained in fixed relation with the diaphragm by means of a set screw 6. The rod 5 may be actuated by electromagnetic mechanism housed in the casing 7. The casing 7 may be attached to a support or spider 8 which in turn may be affixed to the resonator or sound board by means of wood screws 9.

In constructing a loud speaker of this type, I have found that excellent results are obtained by making the cone 2 approximately 15 in diameter and the sound board approximately 24 in diameter. This makes the transverse width of the annular sound board approximately 4 but good results may be obtained by making the sound board of less or greater width than this.

In this type of speaker the central conical diaphragm efliciently reproduces the higher tones and perhaps some of the intermediate tones, while the surrounding annular resonator or sound board efficiently reproduces the lower or bass notes. By reason of the fact that the sound board is made of cork the reproduction of the lower or bass notes is very true and faithful. The lower notes are not only accurately reproduced, but the tonal quality is excellent, the reproduction being soft and mellow.

In a loud speaker'constructed in accordance with the foregoing description, the regenerated or reproduced sound waves are substantially directly proportional both quantitively and qualitatively to the actuating force and the sound so reproduced retains substantially the same balance of high and low tones as the original sound from which the actuating force was derived.

In a companion application Serial No. 79,329, filed January 5, 1926, I have described and claimed a loud speaker having a sounding board made of balsa wood. Loud speakers thus equipped give wonderfully accurate sound reproduction with good tonal quality and balance, but the sound boards are diflicult to make, particularly if built up as a multiple-ply veneer. Balsa wood splinters and breaks in the ply cutting machines and the cut pieces fray at the edges during handling in the mill. Also the completed board is inclined 'to warp unless special expedients are resorted to for holding it in shape.

The cork sheets used in constructing the rim may be purchased in the open market. I have successfully employed sheets of Acco cork made by the Armstrong Cork Company, and have employed sheets and thick. Thinner or thicker sheets may be employed. The material is easily worked and may be cut to the proper size and provided with the beveled edge 4, by means of ,any suitable apparatus. The spider retains the cork in its proper form or shape, and the speaker may be supported on a stand or bracket secured to the spider. The pliancy or fiabbiness of the cork permits it to readily respond to the low frequencies in a narrow rim such as must be employed in the smallersize speakers without reaction, which is not possible with stiffer materials such as wood.

I claim:

1. A loud speaker tympanum having a portion which is freely responsive to the higher frequencies and a portion formed of cork which is freely responsive to the lower frequencies.

2. A'loud speaker tympanum having a sound reproducing rim of cork which is freely responsive to the lower frequencies and a portion within said ri-m which'is freely responsive to the higher frequencies.

v 3. A loud speaker comprising a relatively light and stiff diaphragm, an external cork sound board of greater mass than the diaphragm, and a flexible coupling between the two adapted to permit the diaphragm to respend to relatively high frequencies and adapted to transmit the relatively low frequencies to the sound board.

4. A loud speaker comprising a central relatively light andstiff diaphragm, an external cork sound board. of greater mass than the diaphragm, and a flexible coupling between the two adapted to permit the central diaphragm to respond to relatively high frequencies and adapted to transmit the relatively low frequencies to the sound board.

5. A loud speaker comprising a central conical diaphragm, an external cork sound board of greater mass than the diaphragm, and a flexible coupling between the two adapted to permit the conical diaphragm to respond to relatively high frequencies and adapted to transmit the relatively low frequencies to the sound board.

6. A loud speaker comprising a central conical diaphragm, an external cork sound board and a connection between the conical diaphragm and the sound board adapted to permit the central diaphragm to respond to relatively high frequencies and adapted to transmit the relatively low frequencies to the sound board.

7. A loud speaker comprising a central tending radially beyondthe conical diaphragm and a connection between the conical diaphragm and the sound board adapted to permit the conical diaphragm to respond to relatively high frequencies and adapted to transmit the relatively low frequencies to the sound board. 4

8. A loud speaker comprising a central conical diaphragm having an integral forwardly flaring brim portion, and a cork sound board providing a flange portion extending radially beyond the conical diaphragm, said forwardly flaring brim portion of the conical diaphragm being attached to the sound board.

9. A loud speaker comprising a conical diaphragm provided with a peripheral corrugation forming a hinge portion, and a cork sound board extending radially beyond the conical diaphragm, said hinge portion being secured to said sound board.

10. A loud speaker comprising a cork sound board, and a conical diaphragm flexibly connected thereto so that a portion of the sound board extends radially beyond the conical diaphragm, the flexible connection between the conical diaphragm and the sound board being adapted to permit the conical diaphragm to respond to relatively high frequencies and being adapted to transmit the relatively low frequencies to the sound board.

11. A loud speaker comprising a central conical diaphragm made of paper, an external sound board made of cork and a flexible connection between the two adapted to permit the conical diaphragm ,to respond to relatively high frequencies and adapted to transmit the relatively low frequencies to the sound board.

12. A loud speaker comprising a cork sound board having a central opening, a conical diaphragm mounted in said 0 ening, actuating means for the conical diap ragm, and

means for supporting said actuating means comprising a support attached to the sound board and spanning the central opening thereof. 7

13. A lou'd speaker comprising an annular flat cork sound board having a circular central opening, a conical diaphragm having a circular periphery, said conical diaphragm being mounted in said opening, and a flexible coupling between the conical diaphragm and the sound board adapted to permit the conical diaphragm to respond to relatively high fre uencies and adapted to transmit relative y low frequencies to the sound board.

14. A loud speaker comprising an annular cork sound board having a central opening the edge portion of which is provided with a tapering seat, and a conical diaphragm mounted in said opening, said diaphragm having a forwardly flaring frusto-conical brim portion secured to the sound board on said tapering seat.

15. A loud speaker com rising a flat annular sound boardmade oi cork, said sound board having a central opening the edge portion of which is provided with a tapering seat, and a fibrous conicaLdiaphragm mounted in said opening and having an integral forwardly, projecting portion, a part of said brim portion being attached to the soundboard at said tapering seat.

In'testimony whereof I aflix my si nature.

MARCUS C. HOP INS. 

